1. Field of the Invention
The present invention relates to a liquid crystal display device, a backlight control method and a program, and more particularly, to a liquid crystal display device, a backlight control method and a program, which can control luminance of a backlight in the liquid crystal display device having a touch panel function to reduce power consumption.
2. Description of the Related Art
A liquid crystal display device is a light flat display device, and for example, is widely used for optical touch panels such as a display for cameras, portable information processing apparatuses, bank terminals or the like. Since the liquid crystal display device is a non-light-emitting display, a backlight for illuminating a display screen from a back side thereof is used to enhance visibility and allow usage in a dark place. A fluorescent tube, an LED or the like is used as the backlight.
In a case where a display unit of the liquid crystal display device is used as an input unit of a touch panel type, a finger of a user or a stylus pen which is an input device of a pen type is put in contact with or close to a surface of a liquid crystal panel. In such a touch panel type liquid crystal display device, a position is detected in which such a finger or stylus pen is in contact with or close to the surface of the liquid crystal panel.
More specifically, light emitted from a backlight is reflected from an object, that is, the finger or stylus pen which is in contact with or close to an upper part of the panel, and the reflected light is detected by a sensor (detecting element) which is installed inside of the liquid crystal panel, to thereby determine an input position or area. A variety of data processes are performed according to the determination. Regarding the touch panel type liquid crystal display device is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2009-63803.
Hereinafter, a configuration example of a liquid crystal display device of an optical touch panel type will be described with reference to FIG. 1. An input and output display panel 11 which is shown in an upper left side is a panel having functions of a display unit and a sensor. In a sectional view which is shown in a lower left section, a backlight 12 which is made of a fluorescent tube, an LED or the like is arranged on a rear surface of the input and output display panel 11.
If a finger of a user or the like comes in contact with the input and output display panel 11, sensor detected information is input to a sensor detection information input unit 21. The sensor detection information input unit 21 outputs information on a position in which an object such as a finger is contacted to a data processing unit 22. The data processing unit 22 performs data processing corresponding to a predetermined contact position. For example, a process of changing display data or the like is performed. A command for changing the display data is output from a display control unit 23. The display control unit 23 performs the process of changing the display data of the input and output display panel 11 according to an input from the data processing unit 22.
On the other hand, there is a control processing system of the backlight 12, in addition to the data processing system. A backlight luminance adjusting unit 31 adjusts luminance of the backlight. A backlight light emitting control unit 32 performs an ON/OFF control for a turn-on and turn-off process of the backlight. The backlight is set to an interface of a touch panel type, and is set to repeat turn-on and turn-off (ON/OFF) at a short interval. Accordingly, detection accuracy for a contact position with respect to the panel is enhanced. The backlight light emitting control unit 32 performs the ON/OFF control.
In the input and output display panel 11 having such a sensor, it is known that sensitivity change occurs due to temperature characteristics and secular change of sensitivity of the sensor. Thus, luminance (light intensity) of the backlight 12 is preset to a large value so that contact of a finger or the like can be sufficiently detected even in the case where the sensitivity of the sensor is changed to be lowered and the detection sensitivity is predicted to the minimum.
That is, the backlight luminance adjusting unit 31 is adjusted to be supplied with high electric current so that the luminance of the backlight is preset to a high degree, in order to obtain a sufficient light intensity even though the sensitivity of the sensor is lowered due to the secular change. Thus, in an initial state, excessive power higher than originally necessary power is supplied, and thus, excessive power consumption occurs.
Further, it is similarly known that sensitivity of the sensor is lowered due to temperature change. Thus, the backlight luminance adjusting unit 31 is adjusted so that the luminance of the backlight is preset to a high degree, in order to obtain a sufficient light intensity even though the sensitivity of the sensor is lowered due to the temperature change. Thus, for example, in a state where there is high temperature such as summer, excessive power higher than originally necessary power is supplied, and thus, excessive power consumption occurs.